write operation is initiated to transmit the second byte of data. P3.3 is taken high following the completion of the second write operation. SCLK should idle high between the two write operations. The 80C51/80L51 outputs the serial data in a format that has LSB first. The AD9832 accepts MSB first (the 4 MSBs being the control information, the next 4 bits being the address, while the 8 LSBs contain the data when writing to a destination register). Therefore, the transmit routine of the 80C51/80L51 must consider this format and rearrange the bits so that the MSB is output first.